Different repeat-motif-molecules have been developed to provide an alternative to classical antigen binding molecules, such as immunoglobulins.
Exemplary repeat-motif-molecules are designed ankyrin repeat proteins (DARPins). DARPins can be expressed in functional form in the cytoplasm of E.coli strains. The repeat motif of DARPins comprises a 33-residue amino acid sequence. The repeats comprise a β-turn motif followed by a pair of antiparallel α-helices and a loop leading to the turn of the next repeat. Generally between 1 to more than 30 repeat motifs are present in ankyrin repeat-motif-molecules, whereby 4 to 6 are most frequent.
Kohl et al. (Kohl, A., et al., Proc. Natl. Acad. Sci. USA 100 (2003) 1700-1705) developed an artificial ankyrin repeat module based on the alignment of about 2000 naturally occurring ankyrin repeat sequences. This artificial consensus ankyrin repeat sequence comprises 27 fixed amino acid residues and 6 variable amino acid residues forming a (part of a) binding site (Forrer, P., et al., ChemBioChem 5 (2004) 183-189).
In order to obtain DARPins binding to a predetermined target molecule the variable amino acid residues of the artificial consensus ankyrin repeat sequence are randomized and a specific binder is identified via ribosome display (see e.g. WO 02/020565; Hanes, Proc. Natl. Acad. Sci. USA 94 (1997) 4937-4942).
In US 2009/0148905 antigen binding constructs are reported. Complement factor H-derived short consensus repeat-antibody constructs are reported in WO 2008/135237. Antibody-RNAse-conjugates are reported in WO 2007/122511. A Newcastle Disease Virus comprising a recombinant nucleic acid, wherein the nucleic acid codes for a binding protein that has a therapeutic activity when expressed by the virus-infected tumor cell is reported in US 2008/0206201. In US 2008/0248026 PTEN/AKT methods and compositions relating to BMP are reported. Recombinant expression of proteins in a disulfide-bridged, two-chain form is reported in WO2005/076902 and US 2008/0103098. In WO 2009/068649 antigen-binding constructs are reported.